• Journal of Korea Water Resources Association
• /
• v.43 no.6
• /
• pp.517-524
• /
• 2010

In this study, the 1D apparent shear stress model for vegetated compound open-channel flows was suggested. To consider the effect of momentum exchange between main channel and floodplain, the eddy viscosity concept was used in the present model. The interfacial eddy viscosity in the interface of main channel and floodplain was determined from the 3D Reynolds stress model. The evaluated interfacial eddy viscosity appears to be good agreement with those proposed previously. To investigate the effect of interfacial eddy viscosity, sensitive analysis was carried out. the computed backwater profiles are nearly identical with respect to the value of the interfacial eddy viscosity. However, the discharge conveyed by the floodplain changes is proportional to the interfacial eddy viscosity. Finally, the changes of the interfacial eddy viscosity due to the vegetation density and vegetation height were examined. The computed results of interfacial eddy viscosity are in proportion to the vegetation density and vegetation height, and the interfacial eddy viscosity has a range of $(2-5)\;{\times}\;10^{-4}$.

• Journal of Korea Water Resources Association
• /
• v.30 no.3
• /
• pp.201-210
• /
• 1997

To analyze the flow through open-channel constrictions using $\kappa$-$\varepsilon$ turbulence mode, a numerical model is developed. The simulated results agree well with existing experimental data which attributes to the adequate input of turbulent eddy-viscosity by turbulence model. A stream function and velocity distributions enable the analysis of flow characteristics at the downstream of constriction. Turbulent eddy viscosities over channel are spatially varied with stream pattern. For the evaluation of rapidly varied flow, the eddy-viscosity input by turbulence model is required instead of the empirical effective viscosity to solve a shallow water equation.

• Journal of The Korean Society of Agricultural Engineers
• /
• v.54 no.3
• /
• pp.159-168
• /
• 2012

본 연구에서는 해성 점성토에 대하여 반복 삼축시험을 실시하고 응력-변형률 관계 및 유효응력경로 특성 분석을 통해 동적 변형 및 강도 특성을 조사하였다. 시험에 사용된 시료는 일본 도쿠시마현의 코마츠시마 항 인근에서 채취된 점성토이며, 반복 삼축시험으로 동적 비배수 삼축시험, 동적 비배수 삼축시험 후 동적 삼축변형시험, 다단계 동적 비배수 삼축시험, 동적 삼축 변형시험 등 4종류의 시험을 수행하고, 시험 주파수로서 0.1 및 0.01 Hz을 적용하였다. 본 연구 결과 0.01 Hz로 수행된 동적 삼축시험 결과는 0.1 Hz로 수행된 삼축시험 결과보다 평균유효응력의 감소량이 크며, 반복 하중은 해성 점성토의 구조적 약화를 초래하고 초기 거동시 발생하는 간극수압과 밀접하게 관련이 있는 것으로 나타났다. 또한 미소변형률 영역에서 등가 탄성계수는 시험 횟수가 증가함에 따라 점차 감소하며, 감쇠비는 점차 증가하는 것으로 보아 변형계수는 반복 하중으로 인한 전단변형률의 축척에 따른 변형률 의존 거동에 관련하는 것으로 판단된다.

• Journal of the Korean Geosynthetics Society
• /
• v.5 no.2
• /
• pp.1-8
• /
• 2006

The properties of contaminated soil, contaminants and elapsed time are important considering factors to in-situ soil remediation. Gabr et. al. (1996) derived the solution equation of contaminant concentration ratio as initial one ($C/C_0$) with time and spatial changes in contaminated area which are embedded with vertical drains. The contaminant concentration ratio ($C/C_0$) is analyzed with time and spatial changes as varying the effective diameter, porosity, shape factor, density of contaminated soil, temperature in ground, unit weight and viscosity of contaminants by using FLUSH1 model modified from FLUSH. Results from numerical analysis indicate that the most important factor to the in-situ soil remediation in vertical drain system is the effective diameter of contaminated soil. It also shows that the next important factors are the viscosity of contaminants, porosity of soil, shape of soil, temperature in ground, unit weight of contaminants and density of soil, in order. However, the others except the effective diameter of contaminated soil are insignificant to the soil remediation.

• KSCE Journal of Civil and Environmental Engineering Research
• /
• v.26 no.1A
• /
• pp.45-54
• /
• 2006

To obtain realistic stress-strain relation in concrete, it is necessary to improve the constitutive model for creep and shrinkage of concrete. This study is made up with predicting model of creep using rheological approach and mathematical development which is solution for phenomenon of concrete creep. Long-term deformation components are combined based on traditional 4-parameters model. Creep deformation is obtained adequately using 4-parameters determined by considering aging effect and microprestress among gels. And coefficient of effective viscosity is able to represent both basic creep and total creep included drying creep. This study attempt to establish mathematical model considering effects of aging, hydration, and variations of pore humidity. It can predict both basic creep and total creep. Values of result between prediction and experiment have greater than correlation factor 99%. Additionally experimental results report bad consentaneity with highway design specification adopting FIB MC 90. Rather than those are similar to FIB MC 90 rev.99.

• Proceedings of the KIPE Conference
• /
• 2017.07a
• /
• pp.447-448
• /
• 2017

본 논문은 위치 제어 시스템의 기계 제정수 추정 알고리즘을 제안한다. 추정 대상 제정수는 관성모멘트와 점성 마찰계수, 쿨롱 마찰계수이다. 제정수 추정에 대한 오차를 줄이기 위해, 적분 연산과 정현파의 위치 명령을 사용하였다. 시뮬레이션 및 실험을 통하여 이의 유효성을 입증하였다.

• Journal of the Korean Geotechnical Society
• /
• v.36 no.11
• /
• pp.149-156
• /
• 2020

Permeation grouting effectively enhances soil strength and decreases permeability of soil; however, the flow of grout is heavily affected by anisotropy of hydraulic conductivity in layers. Therefore, this study investigates the effect of permeability anisotropy on the effective radius of horizontal permeation grout using computational fluid dynamics (CFD). We modeled the horizontal permeation grout flow as a two-phase viscous fluid flow in porous media, and the model incorporated the chemical diffusion and the viscosity variation due to hardening. The numerical simulation reveals that the permeability anisotropy shapes the grout bulb to be elliptic and the dissolution-driven diffusion causes a gradual change in grout pore saturation at the edge of the grout bulb. For the grout pore saturations of 10%, 50% and 90%, the horizontal and vertical radii of grout bulb are estimated when the horizontal-to-vertical permeability ratio varies from 0.01 to 100, and the predictive model equations are suggested. This result contributes to more efficient design of injection strategy in formation layers with permeability anisotropy.

• Journal of the Korean Society of Marine Environment & Safety
• /
• v.25 no.5
• /
• pp.627-633
• /
• 2019

This study aimed to predict the resistance and propulsion performance of a ship using computational fluid dynamics (CFD) and a database as well as establish an assessment method for the energy efficiency design index (EEDI) using the results. First, the total resistance of the studied ship is obtained using CFD. A flow analysis is conducted with the free surface and trim and sinkage using a commercial CFD code (STAR-CCM+). The effective power of the ship is assessed based on the CFD results. The quasi-propulsive efficiency is calculated from an empirical prediction equation using experimental data and similar material. Finally, a general calculation program for the EEDI is established based on the hydrodynamic results, ship information for principal particulars, conversion factor of $CO_2$ for fuels, and fuel consumption.

• Transactions of the Korean Society of Mechanical Engineers B
• /
• v.30 no.6 s.249
• /
• pp.546-552
• /
• 2006

In this paper we report fluid flow characteristics of $Al_2O_3$ nanoparicles suspended in water. Especially, the effects of volume fraction with the range of 0.01% to 0.3% and tube diameter with $310{\mu}m$ to 1.735mm on the pressure drop and the effective viscosity of $Al_2O_3$ nanoparicles suspended in water are experimentally investigated. It is shown that the effective viscosity of water-based $Al_2O_3$ nanofluids with 0.1 Vol.% through a circular tube of 1.024mm diameter is increased to about 6%. The effective viscosity from experimental results is compared with that from Einstein model. With the comparison, we show that Einstein model for determining the effective viscosity of nanofluids is not applicable to water-based $Al_2O_3$ nanofluids.

• Journal of the Korean Geotechnical Society
• /
• v.17 no.4
• /
• pp.49-55
• /
• 2001

본 논문에서는 서해안 폐기물 매립지 하부의 점성토와 고화차수재를 재료로 수행된 확산시험 결과와 현장 조건을 적용하여 오염물이동성에 대한 수치해석을 수행하였다. 무기화합물이 하부 차수재와 원지반퇴적층으로 이동되는 일차원 이동 특성을 대상으로 하였으며 일차원 용질이동해석 프로그램 CDFD(convection-dispersion finite difference)를 현장의 비균질한 지층에 이용할 수 있도록 수정하여 적용하였다. 그 결과 원지반점성토를 통한 용질이동 메카니즘에 확산이 기여하는 정도가 50%로 매우 큰 영향을 갖고 있음을 보여주며 원지반 투수계수가 클수록 인공차수층의 필요성이 증대됨을 알 수 있었다.